Solve for $x$ and $y$ using substitution. ${3x+y = -9}$ ${x = 4y+10}$
Answer: Since $x$ has already been solved for, substitute $4y+10$ for $x$ in the first equation. ${3}{(4y+10)}{+ y = -9}$ Simplify and solve for $y$ $12y+30 + y = -9$ $13y+30 = -9$ $13y+30{-30} = -9{-30}$ $13y = -39$ $\dfrac{13y}{{13}} = \dfrac{-39}{{13}}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = 4y+10}\thinspace$ to find $x$ ${x = 4}{(-3)}{ + 10}$ $x = -12 + 10$ ${x = -2}$ You can also plug ${y = -3}$ into $\thinspace {3x+y = -9}\thinspace$ and get the same answer for $x$ : ${3x + }{(-3)}{= -9}$ ${x = -2}$